Rethink everything you know about stretching, form, and even the way you think about training. Photo: Axel Brunst/TandemStock

The Science of Running

You don't have to work harder to get faster—you just have to get smarter about the way you train. We talked to the top researchers and athletes to glean the secrets that professional use to outperform the competition. Over the next month, we'll teach you how to stretch without losing power, turn your form into your secret weapon, and optimize your fueling. You’ll never run the same again.

Because there’s a lot more to running than lacing up your shoes and hitting the pavement

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What makes a runner? To find out, we surveyed 650 of our readers about everything from their training plans to their favorite trail companions. Some of the answers will surprise you—and they may give you the inspiration to set a new PR.

Different parts of our body seem to talk to and influence each other, even when they are far apart and—one might think—unconnected

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One March day in 1894, a woman named Emily Brown squeezed a rubber bulb with her left hand 10 times, as hard as she could. The bulb was attached to an instrument that gauged the strength of her grip. She was establishing a baseline.

Eight times over the next 13 days, Brown did the same contractions, this time with her other hand—essentially putting that hand on a workout program. Her ‘trainer’ was Edward Wheeler Scripture, an American physician and psychologist, who had recently co-founded the American Psychological Association.

On the thirteenth day, Dr. Scripture had Brown squeeze the bulb with her untrained, left hand, and something amazing happened: though she had only worked on the strength of her right hand, Brown had seemingly increased the strength of her left hand by 43 percent.

This effect, often called “cross education,” has been replicated by scientists many times since the nineteenth century. A 2006 analysis of 16 cross-education studies found that the strength of the untrained limb increased about seven percent, on average—about half of the strength gain of the limb that did the workouts.

How far does the phenomenon extend in the body? In the past few years researchers have been exploring that question. What they’ve found is both odd and fascinating. Different parts of our body seem to talk to each other and influence each other, even when they are far apart and—one might think—unconnected. ​More than simply curiosities, these connections could have implications not only for how athletes train but also for how people should rehabilitate after an injury to one side of the body.

“We’re so interconnected, both sides,” says David Behm, a research professor at the School of Human Kinetics and Recreation at Memorial University of Newfoundland in Canada who has co-authored several of the recent studies.

Here are some of the more interesting discoveries:

The Left Leg Knows What the Right Hand Is Doing

One of the most interesting of these findings is that exercising an arm doesn’t just influence the other arm but can actually impact the performance of the lower body.

In one study, researchers found that soon after young men and women performed rounds of a fatiguing handgrip exercise, the ability of their plantar flexor (ankle-area) muscles to produce force “significantly decreased" by two measures, according to a 2013 study in the European Journal of Applied Physiology. Another study found that fatiguing the elbow flexors meant that test subjects couldn’t fully activate their quadricep muscles, found a 2014 study in the journal Applied Physiology, Nutrition, and Metabolism.

“[T]he bottom line is the fatigue does seem to ‘travel’ from one muscle group to another, and mainly, from upper to lower body rather than from lower body to upper body,” writes Israel Halperin, the lead author of the 2014 study and a PhD scholar with Edith-Cowan University and the Australian Institute of Sport. Or at least it manifests differently in the upper body.

So what’s going on?

When you do those bicep curls, your biceps aren’t the only thing getting a workout. Your central nervous system gets a workout, too, researchers believe, as it deals with all of the information that it’s processing—contracting one muscle, relaxing another, balancing your body, keeping a firm grip. That’s a fair bit of work. As a result, the nervous system gets a little fatigued, says Behm.

Now let’s say you drop the dumbbells and bust out the door for a run. Lower-body muscle groups like the quadriceps are larger than, say, elbow flexors and biceps. They have more motor units—the places in your legs where the electrical signal is converted to movement—and also have a larger percentage of fast-twitch muscle fibers, says Behm. All of these factors mean that using them puts a strain on a nervous system that’s already a little tired, the theory goes. It’s similar to what happens when the lights dim in a small town after a big factory turns on its machinery.

How all of this is connected is still not fully known. While researchers understand pretty well how our muscles function, our wiring is even more complicated. “Generally we know that there are changes and inhibitions that happen in both the brain and the spinal cord,” Behm says. “But we’re not exactly sure of the pathway for it.”

A blend of factors, though, may cause a non-local muscle to tire. “Mainly, we are talking about neural (brain and spinal cord), peripheral (various metabolites), biochemical (accumulated fatigue in stabilization muscles required to stabilize the body during the tests) and psychological (deficits in motivation to complete the task with much effort) pathways, and their interaction,” says Halperin.

Stretching

Stretching, too, has been found to produce intriguing “crossover” effects. In one study by Behm and colleagues, participants experienced “significant” increases of eight-to-nine percent in the range of motion of their shoulders after they performed static and dynamic stretching in their lower bodies.

Conversely, the participants experienced more than a five percent increase in range of motion of their hip flexors after they performed static stretches on their upper body, according to a 2016 study in the European Journal of Applied Physiology.

“Stretch one part of your body and another part becomes more flexible,” says Behm.

In another study, 14 crew rowers engaged in multiple days of stretching sessions in which they did several repetitions of hip-flexor stretches, either static or dynamic. During each session, one hip-flexor was stretched; the other one wasn’t. Range of motion of each hip flexor was measured. The results: depending on the type of stretch the range of motion of the unstretched limb either was nearly as good, or even better, than the stretched limb.

The reason the unexercised limb experienced such benefits has to do with “increased stretch tolerance,” say researchers. “Stretching can be uncomfortable,” Behm explains. “You pull that muscle and it’s not a very nice feeling, all that tension on your muscle. But if you’ve already stretched, you’ve accommodated that in a certain limb.” The discomfort is now expected; it becomes more manageable, and you allow yourself to settle into it.

“It makes sense that if you increase the range of motion in one limb, the nervous system is going to mimic that in the other,” says Arnold Nelson, a professor in the Department of Kinesiology at Louisiana State University who has been involved in several other stretching studies. “You don’t want to take a four-foot stride with one limb, and not be able to do that with the other. The body wants to be able to keep everything in balance, as best as it can.”

Information like this could benefit high-end athletes. Studies show that static stretching produces minor, short-term impairments in performance, the kind of impairments most of us gladly trade off for the benefits that stretching provides. But running five percent slower could spell disaster for a thoroughbred Olympic sprinter. But if that same sprinter stretched his shoulders instead of his legs, right before he stepped into the blocks? In theory, he would gain increased range of motion in his legs, with no downside, according to Behm.

Stretching one limb can affect the opposite (aka contralateral) limb, too. In one study researchers had 13 people stretch one of their calves four times per day for 30 seconds each, a few times per week for 10 weeks. They didn’t stretch the other calf at all. Meanwhile, a control group did no stretching to either calf.

Just as expected, after 10 weeks the stretched calf experienced significant increases both in range of motion and strength—29 percent stronger. While the unstretched calf didn’t gain any range of motion (it actually fell by one percent), the lazy calf nonetheless got 11-percent stronger, according to the 2012 study in the Journal of Strength and Conditioning Research.

A ten-week study isn’t enough time to build much muscle mass, says Nelson, the lead author. Instead, “most of the strength increase is in neural components: you learn to do better synchronization, better use of activation of the muscle itself.” And that’s something that even the passive leg apparently can learn—at least in part.

Some Disagreement

Studies have found many more effects on the lower body than on the upper body, leading to some disagreement among researchers about whether the phenomenon really operates both ways—that is, if what happens in the lower limbs really affects the upper limbs. Behm thinks it does.

In a study last year, he and colleagues had 18 young men who were weight training regularly perform knee extensions until those muscles were exhausted. Then the men’s elbow joint strength was tested by doing several repetitions of an exercise. “The first few repetitions we didn’t see it, but we did see it in the last six” repetitions, when the men showed about a five percent loss of strength, Behm says. In other words, the men did fine with a few reps, but flagged down the stretch.

This, too, has implications for training.

“If you’re an athlete and are wanting to get the best training possible, and you wonder if you can go for a run then do an upper-body workout, the answer is ‘no,’” Behm says. “If you’re an elite athlete, 5-to-10 percent (impairment) every day could affect your training outcomes.”

Why does this happen? “It goes back to the mental energy that you need” to perform a task—what Behm calls “neural drive.” After having used the big muscles of the lower leg on, say, a strong run, the nervous system is pretty fatigued. You can power through a few repetitions of an upper-body exercise. But after a few more, you start to crumble. “The mental fatigue, the mental exertion from a hard run will impair or cause deficits to your upper body when you try to lift weights.”

Putting It to Use

These findings could help accelerate recovery for those people—athletes and otherwise—who have sustained injuries to one side of their body, researchers say.

Let’s say you’ve broken your right leg skiing and now wear a cast on it. If you want to minimize strength loss and rebound from the injury as fast as possible, a great idea would be to exercise your uninjured, left leg—including doing some stretching. True, the casted leg muscles would still atrophy. But with the stretches “you might at least be able to maintain something—it’s only neural, but at least it’s something,” says Nelson.

What’s more, says Behm, by keeping the other leg active, “the central nervous system’s ability to signal that muscle would still be high.” Roughly put, the nervous system grows dull without use, too. But if you keep the lines of communication open and sharp, when that is removed, you won’t have to rebuild that network from scratch. Yes, your muscles will still need rebuilding, but you will be able to recruit those fast-twitch motor units, enabling you to more quickly jump back into training and activities.

Until a few years ago, the accepted wisdom for those looking to improve performance was just to run more, train smarter, or lose weight. Now, you might have to rethink how you run.

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A few years ago, Blue Benadum was a 29-year-old with a marathon PR of 2 hours, 42 minutes and change. Though he knew this put him in the one percent category among marathoners, Benadum, who’d always shown superior ability in every sport he’d pursued, felt he could run faster. No matter how much he trained, however, he couldn’t break 2:42. He estimates he ran 2:42-something at least twelve times. It began to feel like a curse.

Frustrated, Benadum took a VO2-max test to gain some insight into his fitness potential. He blew a 85, the highest score ever recorded in running coach Richard Diaz’s testing center in Camarillo, California. (For reference, 85 puts Benadum in the same league as guys like Lance Armstrong and Steve Prefontaine.) Diaz, who hosts a weekly podcast on running, assumed with that result Benadum would likely have a marathon best somewhere between 2:14 and 2:20. When Benadum told him that he wasn’t even remotely close to hitting those times, Diaz had one thing to say.

“That means you run like shit.”

This was news to Benadum.

“I was, like, this guy is bold,” Benadum said. “I’d never met him before and he’s telling me I run like shit.”

He had always been complimented by fellow runners on his nice, even stride. He’d never had any serious injuries. Even though he was seemingly unable to get faster, he knew he was pretty damn fast. Benadum figured Diaz didn’t know what he was talking about.

But when Diaz performed a gait analysis and showed him the footage, Benadum could tell something was off. He was overstriding and heel-striking. His form looked nothing like that of the Kenyans who were the fastest runners on the planet. He told Diaz to film him again; he was sure that his gait would improve if he ran closer to his marathon pace.

“I knew it didn’t look right, but I told Rich to let me do it again at 6-minute mile pace and that I’d be better,” Benadum said. “And I was actually worse when we looked at the second video. That’s when he got my attention and, for the next three years, I apprenticed under him.”

Diaz’s approach to coaching prioritizes solid biomechanics above all else. His tenets on what constitutes good form will sound familiar to those who have been following the discussion in recent years: mid-foot strike is best; ground contact should be as near to under center of mass as possible; runners should have a slight forward lean in their stride–from the ground, not from the hip; your arms shouldn’t cross the center of your body.

For Benadum, that meant he had to change everything about his stride–from the way his feet were hitting the ground to the way he swung his arms as he ran. It was a difficult adjustment, but he had the benefit of knowing he’d already tried virtually everything else.

“I had run 35 marathons before changing my form. And, dude, I was committed to getting better. I read every magazine, tried different programs, different running volumes, different speed workouts, and I could not break 2:42.” Benadum said. “But after a year of working on my form, my times started to progress: 2:38, 2:35, 2:28, 2:24, 2:23. When I broke to 2:40, I was like ‘Oh, wow, there’s something to this.’ When I got down to 2:30, I was like, ‘You’ve got to be kidding me.’ To me it became like, I have to teach everybody this!”

He has since been trying to do just that. Bendaum, now 35, supplemented his multiyear apprenticeship under Diaz by taking USATF’s coaching certification program and has since founded an elite Los Angeles-based running team called the L.A. Speed Project.

Benadum’s story might give hope to some runners who worry that their race times have plateaued, but some are skeptical. Up until a few years ago, the accepted wisdom for those looking to improve performance was just to run more. Or train smarter. Or lose weight. Getting faster was about how you trained, not how you ran. While “solid fundamentals” are considered crucial for anyone looking to drive a golf ball 250 yards straight down the fairway, or become a 90 percent free throw shooter, with running, the assumption has always been that everybody already pretty much knows how to do it. Running, in other words, is not something you have to learn.

Challenging that assumption doesn’t come without its risks. If you’ve been a heel-striker all your life and you suddenly try to change that, you will be redistributing the stress loads on your feet and legs, which, at least in the short term, makes you more susceptible to getting hurt. (There’s a reason why more than 150 thousand claims were filed in the Vibram FiveFingers case.)

Benadum is a case in point. In his first year of altering his form, he overcompensated for his inefficient heel-strike by accidentally adopting the opposite problem of running too far up on his toes. He says he got injured frequently during this time, but figured such temporary setbacks were part of the process. As he puts it, “When you’re learning something new, you’re gonna screw it up.”

Benadum’s persistence paid off, but not every runner who changed their technique has been as fortunate.

In a 2010 New Yorker article, Jennifer Kahn profiled Dathan Ritzenhein, arguably the most promising American distance runner at the time. Although Ritzenhein was good enough to vanquish all of his stateside competition, his coach, Alberto Salazar, told him that the only way he would have a chance against the top Kenyans and Ethiopians was to go from being a heel-striker to a forefoot runner.

Salazar also wanted Ritz to improve his posture. Unlike paragon striders Kenenisa Bekele and Haile Gebrselassie, who ran with their torso, hips and feet evenly aligned, Ritzenhein had a tendency to kick his feet out too far in front of him when he ran; he was a “sitter.” According to Salazar, it was slowing him down.

From the start, Salazar was open about the fact that tweaking Ritz’s form could lead to injury, but Ritz was willing to give it a try to get to the next level.

That next level proved elusive, however. Although Ritzenhein did run an impressive 2:07:47 at the 2012 Chicago Marathon, his gait adjustment was accompanied by a slew of injuries, from sesamoiditis (pain in the ball of the foot) to repeated stress fractures, that kept him from competing. His Chicago time from 2012 only garnered him 9th place.

“When I came to Alberto, I thought I was done being hurt,” Ritzenhein says in the New Yorker article. “But this is the longest cycle of injuries that I’ve ever had: probably by double, or even triple.”

Ritzenhein is clearly not your typical runner, but his example suggests that aggressively changing the mechanics of how you run isn’t always a good idea, at least when you’ve already been having moderate, injury-free, success with how you run naturally. (Most of Ritz’s fastest performances came in 2009, before the extensive overhaul of his running style.) It’s worth noting that the majority of Diaz’s clients seek his advice not because they want to get faster, but because they’ve been getting hurt. For them, the decision to change their form is an easy one to make–it’s either that or quit running altogether.

Terry Crawford, the director USATF’s coaching program and formerly a head coach of the women’s track U.S. Olympic team, believes that you can work on your form as long as the process is gradual, like slowly building up mileage.

“I don’t think there’s a huge risk in trying to improve running style, if it’s based on becoming more efficient, but it shouldn’t be an overnight change,” she says. “There should be a progression of skill acquisition. And understanding body movements. Even though you don’t need extensive knowledge about muscle structure, it would still be wise to say, okay, where am I going to be putting additional stress if I change my running style?”

Of course, such awareness in itself is no guarantee that you won’t get injured anyway.

“If you have a 10K runner who is a flatfooted heel-striker, and someone tells them they can be more efficient and run much faster if they got up on the ball of their foot, and then they do that for 10K, then they’re probably going to get muscle cramps and maybe strain a calf muscle, because they’ve never used those muscles in that fashion,” Crawford says.

Whether or not healthy runners are willing to risk that strained calf, or worse, will ultimately depend on why they run. Benadum and Ritzenhein were highly competitive athletes willing to try anything to get faster. Both had to contend with injury as a result of changing their form, which might be a deal-breaker for those who are more concerned with consistently getting in their weekly jog than being in the first corral at Boston.

And even those who do compete at the top level don’t all have textbook form. Most do not. Paula Radcliffe, the women’s marathon world record holder, was always a picture of arm-flailing, head-bobbing agony late in the race, while Meb Keflezghi is just one of many elite runners who are noted heel strikers. For every champion runner who represents the ideal–Diaz says right now it’s Galen Rupp, Salazar’s current protégé–there will be someone who has been having great success with a more unorthodox style. Another athlete who Diaz reprimanded for “running like shit” is multiple Olympic gold medalist Michael Johnson.

Needless to say, this complicates the debate on coaching form.

“There can be runners with all types of different running styles, because running style is often determined by your body structure,” Crawford says. “You don’t want to teach a set model. You don’t want to say everyone should run like Justin Gatlin because he’s one of the fastest people in the world. Or Usain Bolt. Because your efficiency has a lot to do with your body size and structure. One of the reasons Usain Bolt runs the way he does is because he’s 6’ 5”. You wouldn’t tell a five foot person to model their body movements after Usain Bolt.”

I suggested to Crawford that, to some extent, this challenges the idea that good running form can be taught.

Crawford agrees, but claims that there are some basic mechanical principles–keeping your body parts aligned with your center of gravity, not leaning too far back or swinging your arms side to side–that are useful to everyone interested in making small improvements to their form. For most amateurs, however, Crawford doesn’t think it needs to be a major priority.

“In terms of how we work with our elite athletes, yes, they’re going to get down to the finer points of analyzing form and technique, but that’s not anything that the average runner needs to be overly concerned with,” Crawford said. “The average runner should be concerned with a running style that will increase their efficiency, prevent them from getting hurt, and increase their pleasure.”

Fortunate is the athlete for whom those three things are mutually inclusive.

Breaking down the latest research and what it means for every kind of runner

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From World War II until the late 1990s, athletes and daily plodders alike were told that the key to flexibility, injury reduction, and better performance was to stretch and hold. (Think of the old hurdler’s sit-and-reach.)

Then in the late 1990s the pendulum swung: researchers found that performance decreased when people exercised right after this type of “static stretching,” when measured by power and force. One of these researchers, David Behm, found that those who held long static stretches before working out suffered from decreased balance and slower reaction times when they exercised immediately after stretching.

Today, most people who stretch before working out now perform “dynamic stretching” instead, which includes movements like crab walks, leg swings, and “Frankenstein” leg raises. But Behm says this may be the wrong approach as well and the best way to stretch before exercise may be more nuanced.

Behm is a research professor at the School of Human Kinetics and Recreation at Memorial University of Newfoundland in Canada and much of his work is focused on what happens to muscles during exercise. But he first started thinking about stretching more than 15 years ago, when he first read a study that that found impairments in performance after using stretching as a warm-up. Behm wasn’t just academically curious. The doctor had a brief career as a professional football player. (“One might say that I had a cup of coffee in the Canadian Football League,” he jokes). As a fullback, he often tried to make up for a lack of speed with strength training and lots of stretching, which likely made him the only guy in the CFL who could squat 500 pounds but also do the splits.

In a new study, Behm and colleagues wanted to know if previous research mimicked how people limber up in the real world—and whether the findings and recommendations that stemmed from these studies thus were valid.

To do so, Behm and his co-authors dissected more than 200 stretching studies published in English between 1989 and 2014. They examined not only the type of stretching, but also the duration of the stretch.

The researchers immediately found problems. Participants were almost always tested in exercise after as much as 30 minutes of stretching. “But who does 30 minutes of stretching?” he asked. (Behm says he, too, was guilty of designing similar studies.)

What’s more, participants often were told to hold stretches for long durations—at least one minute per muscle group. People might do that during yoga class, but rarely right before they exercise, he points out.

When participants showed drops in performance, authors blamed static stretching instead of asking whether extended periods of static stretching might have caused the impairment. The new study doesn’t spare dynamic stretching, either. When the researchers looked at 48 studies that together measured 80 kinds of after-stretching performance—from sprint speed to jump height—they found only trivial positive changes. “Generally, not much happened,” said Behm.

The resulting article appeared in December online in the journal Applied Physiology, Nutrition, and Metabolism.

Here are some more findings, and some new stretching advice from Behm:

Stretching: Do It

In case you’re feeling whipsawed by all the advice, here’s the upshot: keep stretching. The benefits indeed seem to outweigh the costs, in terms of performance, range of motion, and injury reduction, the study found. Of course, to see any benefits, stretch the muscles relevant to your activity.

Do It for Five or More Minutes

To reduce injuries, you’ve probably got to stretch for more than five minutes in total, doing a few different stretches. When you do, the benefits of static stretching for helping your range of motion and reducing injury to your muscles “at least balance, or may outweigh” any slips in your performance you see, according to the authors.

Go Long…But Not If You Go Long

Duration—how long you should hold that static stretch—has created more confusion than perhaps any other factor around stretching. Studies in North America and Australia have found that holding a pose for a minute or longer can lead to between a five- and 7.5 percent impairment in various measures of performance, when exercise is performed immediately after the long stretches, says Behm.

Don’t let that stop you from doing deep stretching. “What you really want to do, if you’re a stiff old man, or -woman, or young person, you should do longer stretching, but you shouldn’t be doing it right before you do your sport,” Behm advises. Yoga is great—just don’t do a class prior a six-mile run. Think of deep stretching as another conditioning exercise more akin to, say, bench press, says Behm—and you wouldn’t do five sets of bench press twice in one day.

Behm recommends incorporating some controlled movement into your pre-workout routine. Dynamic stretching can be done close to your start of the activity.

Danny McMillian, a clinical associate professor at the University of Puget Sound who has written about stretching, agreed with the paper on this. “Use SS (static stretching) as you see fit, but respect the fact that it might decrease nerve to muscle responsiveness. Therefore, follow SS with movements (and rate/loading of movement) that mimic your sport,” McMillian wrote in an email.

Get in the Goldilocks Zone

Just as we’re not all the same, and not at the same level, not every person should be doing the same stretching, says Behm.

Consider Olympic sprinter Usain Bolt. He’s a high-performance machine—a Ferrari, says Behm, who talks about Bolt in his smart 2014 TedX talk. Bolt is only interested in performance. He wants to be taut, tight, all suspension. He has less than 1/10 of a second to land, regroup and explode upward again.

For an elite like Bolt, static stretching right before a race would be a disaster, says Behm. After all, add 5 percent to Bolt’s time in the Olympics and he becomes Gerald Phiri of Zambia, who came in 15th place, or second-to-last, in the semi-finals, says Behm in his talk. “Five percent is the difference between celebrity and anonymity. And it cost this guy millions of dollars.”

The difference, of course, is that the rest of us aren’t Bolt. And we’re not Ferraris. “If you’re an elite athlete, then you might compromise your health for performance. Elite athletes are not always the epitome of health,” he says.

If you want to be healthy and fit for the long haul, don’t be a Ferarri; be a Cadillac, says Behm. Cadillacs have soft suspension. When you hit a pothole in a Caddie, it absorbs the insult and keeps moving, he says. “You want your muscles and tendons to absorb the forces, so you're joints aren’t taking a lot of beating.”

To be a Cadillac, “Strive to be in the Goldilocks Zone,” says Behm. “Goldilocks Zone means you want to have muscles that are just tight enough so that you get an efficient transfer of energy when you hit and go, in whatever sport you’re doing. “But you want muscles that are just flexible enough, that it doesn’t impair your stride length.”

How do you achieve that?

As part of your warm-up, Behm suggests doing four static stretches of six seconds each, in the relevant muscle groups you’ll be using. Combine that with some dynamic stretches, “And you should be fine. You should be in that Goldilocks Zone.”

Hold That Stretch Longer Before You Hit the Mountains

Eccentric exercise—squash, downhill running—can tear up muscles. (It’s why your quads are fried after coming down the mountain on that weekend backpacking trip.) In their review, researchers found that static stretching showed a moderate performance benefit at moderate muscle lengths. Translation: take a few more static stretches when prepping to do eccentric activities in which the muscle lengthens as it is stressed—stuff like hiking downhill.

And what does Behm himself do?

“When I got to play tennis, I stretch my hamstrings, my quads, my groin, my adductors, and then I’d stretch my shoulder joint and lower back,” he says. “Usually I’d hold them about 20 seconds each—that’s about seven minutes of stretching” when added up, he says. Next, Behm will do some dynamic stretching—swinging his leg from side to side, for instance. Finally, he’ll step onto the court and slowly, easily begin to hit balls to warm up.

As Behm holds that static stretch for 20 seconds, his subsequent performance on the court might decrease modestly. The question recreational athletes need to ask themselves is, “What’s the cost-benefit analysis?” he says. If you’re a fraction slower to the ball, or you hit that ball a tiny bit slower, “Well, who the hell cares?” he says. “Does it really make a difference in my game? Probably not.

“But it might make make a difference in whether I get injured or not.”

We can all get obsessive about our daily workouts. When does obsession turn to addiction?

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A good day for Katherine Schreiber begins with an hour of yoga. Without a morning stretch, “I just don’t feel okay in my skin,” she says. A health and fitness writer who lives in Manhattan, Schreiber leaves a yoga mat stretched out on the floor of her apartment at all times, “just in case.” After yoga Schreiber will usually head to the gym for a quick hour or so of mixed exercise, “cardio and core,” before heading to work.

Once several years ago, according to Schreiber, the soft tissue inside one of her spinal disks escaped its enclosure. The resulting herniated disk compressed a nerve running along the nearest vertebrae, creating throbbing pain in her lower back and intermittent, shooting pains down her legs. “The doctor said I needed surgery,” Schreiber remembers, “but there was no way I could take the time off from exercising.” Schreiber, who has structured her life around exercising, is addicted to her workouts. Her apartment is minimally furnished and instead boasts free weights, a TRX machine, a body bar, and spin bike, “and I have an elliptical coming,” she says. Schreiber relies on her routine to feel okay, and the thought of missing a workout causes extreme anxiety. As a consequence, she holds memberships to two separate gyms in Manhattan, so she can workout at nearly any time, regardless of where in town she finds herself.

Told she needed surgery, Schreiber instead hit the gym. “I had a herniated disk for over a year and I went to the gym everyday,” she says. “Hunched over” an elliptical machine, Schreiber worked out in agony. “I couldn’t even hold my back upright,” she remembers. “It was excruciating.”

As it is for most living creatures, movement is a fundamental part of daily life. It is, or should be, as natural as eating or sleeping. In the developed world, though it clearly is not. We’re constantly told that too many of us are inert. But now a select few are too active. As a sedentary society struggling to reckon with the confining world we have built, our relationship to movement lurches between extremes. Eighty percent of us do not exercise regularly—and a small but notable portion of the rest may exercise too much. The research is limited but the best estimate—from a population study in Hungary— suggests that three percent of regular exercisers are exercise addicted. If that rate holds for the U.S., nearly two million Americans could have an unhealthy dependence on their daily workout. These millions are apt to exercise to the exclusion of friends and family and the loss of work and social relationships. Sometimes they will cause themselves intense and possibly irreversible physical harm. And they cannot stop. Small reviews of dedicated athletes paint a more troubling picture: as many as one out of every five amateur runners could be exercise addicted. For marathoners and triathletes that number is one in two.

Schreiber is tall, and blond, with a wide, friendly smile, and the built of an athlete. She has, she believes, struggled to control her dependence on exercise for more than a decade. In that time she has experienced several of the “wake-up call” moments familiar to addicts with more common addictions. She recorded one salient post for Addiction.com. The wake-up came one day when a stress fracture of her left foot, “got so painful that I could no longer run nor get on an elliptical without agony pulsing from my toe to my knee,” she wrote. That injury proved “a blessing in disguise” forcing her to step off the treadmill of her regular routine and downgrade to less activity. Nevertheless, she concedes in the post, she continued to exercise everyday, her fractured foot encased in a plastic surgical boot.

If given the choice a rat will run. A lot. When housed in a cage with a wheel a rat will run at night, “more and more and more,” says Ben Greenwood, a neuroscientist and exercise physiologist at the University of Colorado-Boulder. In rodents, as in humans, exercise burns up stress hormones—cortisol in humans, corticosterone in rats—and triggers the release of pleasant and potentially addicting chemicals, like endogenous morphine. A few weeks of exercise will lead to increased activity in the neurons of a rat brain’s pleasure and reward networks, according to Greenwood’s research, and an almost simultaneous downgrade in the sensitivity of neurons implicated in anxiety and depression. Not surprisingly, “rats like to run,” says Greenwood. “And if you take their wheels away they develop anxiety.”

Exercise dependence has been called a “positive addiction.” But that’s a stretch. The severe addict is compelled to exercise two, three, sometimes more than four hours a day, everyday. Often a traumatic event—the fracturing of an arm, or passing out in a spin class, both actual examples—can act as a wake up call. But like any addiction, cessation can lead to withdrawal, symptoms which include nausea, insomnia, anxiety, anger, and irritability. Tolerance to the exercise dose, meanwhile, forces the addict into increasingly longer or harder workouts. Some will go into debt pursuing their activity. Others will be told by a doctor that, without rest, they will end up in a wheelchair or worse.

“They know they need to cut down, but they can’t,” says Heather Hasenblas, an exercise psychologist who studies exercise addiction at the University of Florida-Gainesville. Even those who do cut back, “reduce how much they exercise but they keep going,” she says. Those unable to switch activities after an injury are often in constant pain, “but it is worth it to them because the alternative is intolerable.”

Schreiber’s addiction began gradually, as most exercise addictions seem to. “When I started exercising regularly it was very easy to get away with over-doing it,” Schreiber told me. “It was a behavior that seemed healthy.” The phenomenon may work a bit like this: we all have stressors in our lives, large or small, that we must cope with. You like to be healthy, to do things that are good for you. So when you get anxious or upset, you don’t grab a beer, instead you lace up, clip in, pull down, or whatever else makes you feel good and productive. Rather quickly the work pays off: circulating stress hormone levels drop soon after exercise has begun and stay low, especially at night. If you are anything like a rat, you will also experience a lowered stress response in the future. For a lot of people the story ends there.

“Many people can exercise two or three hours a day safely,” says Hasenblas. But others, when they arrive home and towel off, find that their stressors waited for them. Anxiety, though dulled, returns, and the next time they head out, they stay out longer. The stress melts away and the endorphins kick in and the cycle repeats itself. Other coping mechanisms with less immediate physiological feedback, like devoting time to friends or family or community, tend to fall away.

“For most people who are addicted it’s about escaping the problems in their life,” says Mark Griffith, a behavioral addiction researcher at Nottingham Trent University in the United Kingdom. “The paradox is that mood modification is an absolutely fundamental core to addictive behavior. People use the behavior either to get buzzed up, to get high, aroused, excited—or to do the exact opposite, to tranquilize, to escape, to numb, to relax.” It is self medication. “And people use chemicals in the same way to produce a reliable, consistent change in mood. Exercise is one of those activities that when you are absolutely in the moment you can’t think about anything else.” That’s one of the things that makes exercise so great, and potentially addictive.

Exercise dependence may be unique among addictions (save workaholism) in that a physical and emotional dependence builds within the confines of a socially-acceptable behavior. “Nobody’s ever like—oh you smoked three packs? Awesome!” says Schrieber. This can make it easy to begin an addiction, and hard to tell when a line has been crossed. Inevitably, exercise provides all the rewards necessary for addiction: physical, psychological, social, and, if you are a professional, financial. “Each of these is going to contribute to your addiction,” says Griffith.

To Hausenblas the difference between safe and unhealthy exercise hinges on “the underlying motivation.” Is it to escape—or to achieve? To punish, or heal?

The handful of studies that have examined exercise addiction in professional or elite athletes suggest that they may not be immune to addiction. Far from it. In a small study of ultrarunners, Griffith only found three percent that met his criteria for exercise dependence. However, when he looked at a larger group of students training for careers in sports, the number of addicted jumped to nearly seven percent. Reported rates of addiction in competitive amateur runners have varied from 22 percent to nearly 40 percent, depending on the study population and the testing protocol used. A survey of more than two hundred triathletes selected randomly from international competitions classified half as highly exercise dependent.

To Schreiber the hinge between healthy preoccupation and unhealthy obsession is flexibility. Does a committed exerciser “maintain their schedule when they have a stress fracture or tear a muscle?” she asks. “Can they take a break? If they do, can they sleep?” Schreiber writes about addiction professionally and may understand her disease better than most. (She recently co-wrote, with Heather Hausenbla, the first popular manual on the disease). Yet she still finds herself absolutely compelled to exercise. “Relapses are involved,” she says, and admits that she hasn’t taken a day off from exercise in years.

As most of us try to increase our time spent moving within or between stationary jobs, incapacitating commutes, and sedentary social activities, we all must struggle to find the right balance between no movement and too much.

The Latest on Low-Carb, High-Fat Diets

We've finally got the data

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In December, racewalker Evan Dunfee notched a huge personal best at a 50-kilometer race in Australia, smashing the Canadian record and punching his ticket to the Rio Olympics this summer. Just a few weeks earlier, he’d completed a three-week block of intense training on a diet of 75 to 80 percent fat, fueled by pre-workout boiled eggs and nutballs—“nuts, cocoa, and I’m not sure what else to hold them together,” he recalls, “but they were alright”—and mid-workout cheese and birthday cake.

Yet another anecdote in the ongoing low-carb, high-fat (LCHF) wars, you might say. But Dunfee is actually part of an ambitious multi-month study at the Australian Institute of Sport featuring an international group of Olympic-bound race walkers randomized to different diets. Along with the recent publication of a new study on the metabolism of fat-adapted ultra-runners and triathletes, the research marks the beginning of a new phase in the raucous debate over whether it’s possible, or even preferable, to compete as a high-level endurance athlete on a LCHF diet. In short: we’re finally getting some data.

Louise Burke, the head of nutrition science at AIS, is leading the Australian study. She and her colleagues spent more than a decade studying LCHF diets in search of a competitive advantage before concluding, in 2006, that the approach was a dead-end. But as the concept’s popularity surged across the blogosphere over the past few years, she took notice. “I think it is important to keep your finger on the pulse of what athletes are talking about or trying, and what new theories and ideas are being promoted,” she says.

The basic logic of the high-fat approach is simple. An average person can store about 2,500 calories of carbohydrates, enough to last a couple of hours; in contrast, even the slimmest of athletes has something like 50,000 calories of fat ready and waiting. If, by subsisting on a high-fat diet, you can train the body to burn primarily fat rather than carbohydrate, then you’ll never run out of fuel, and you’ll be freed from the need to suck down nausea-inducing quantities of gels and sports drinks.

The theory is fine. But in practice, what Burke and her colleagues found in the 1990s and 2000s was that by ramping up fat burning, you also curb carb-burning. That’s a problem, because carbohydrates provide the rapid fuel needed for high-intensity bursts. A 2006 study at Tim Noakes’s lab in South Africa had fat-adapted cyclists ride a 100-kilometer time trial interspersed with 4-kilometer surges and 1-kilometer sprints, simulating the thrust and parry of a Tour de France stage. While the overall times were similar, the high-fat cyclists were significantly slower on the race-defining sprints. That’s the study that Burke initially dubbed the “nail in the coffin” for LCHF.

There are a number of possible counter arguments to this objection. One is that the subjects hadn’t spent enough time adapting to a high-fat diet to fully reap the benefits. Another is that some people—ultrarunners, for example, particularly those whose primarily goal is simply to complete the distance—would gladly sacrifice the ability to charge up a hill or sprint to the finish in exchange for easier in-race refueling. But without data, it’s hard to draw firm conclusions either way.

To address the problem of adaptation time, a team led by Jeff Volek of Ohio State University recruited 20 elite ultra runners and Ironman triathletes, half of whom had voluntarily switched to a LCHF diet months or years earlier, and brought them to the lab for testing. The results, published this month in the journal Metabolism, showed that the fat-adapted runners were able to burn fat twice as quickly as the non-fat-adapted control group. During a three-hour treadmill run at a moderate pace, they relied on fat for 88 percent of their energy, compared to 56 percent for the controls. “The rates of fat burning are extraordinary based on conventional wisdom,” Volek says.

That was the good news. The more puzzling finding was that the fat-adapted runners still seemed to consume glycogen—the form in which muscles store carbohydrate—at exactly the same rate as the non-fat-adapted runners. “We can only speculate as to the reason they bother breaking down glycogen when it is not terminally oxidized,” Volek says. On the surface, that seems like a problem: If you’re burning the same amount of carbohydrate, do you really have an advantage? But observers like Paul Laursen, an exercise scientist with High Performance Sport New Zealand who was not involved in the study, see the results as further evidence of the adaptations that take place: “Things in the LCHF athlete work differently,” he says, “but better.”

Of course, no Olympic medals are awarded for having the most interesting metabolism. Actual endurance performance was not measured in the study, and the diets of the subjects were estimated by having them keep food logs for three days. These are not trivial details. One widely circulated article about elite endurance athletes turning to high-fat diets cited triathlete Simon Whitfield and Tour de France cyclist Dave Zabriskie as converts. But Whitfield, on his blog, estimated his dietary breakdown as 50 percent carbohydrate, 30 percent protein, and just 20 percent fat—far from the 75 percent theoretically required for LCHF territory. Zabriskie, meanwhile, says that his high-fat experiment was interesting but hardly ergogenic: “For long easy training, it’s good. For day-after-day racing like the Tour, you have to eat the carbs.”

That’s the gap that Burke and her colleagues at AIS hope to fill with their study of race walkers. While race walking is a relatively obscure sport, it may be a good fit for LCHF: the 50-kilometer race is the longest track-and-field event, lasting just under four hours, and the rules prevent anyone from breaking into an all-out sprint. The community of walkers is also tightly knit, which enabled Burke to recruit Olympic-caliber walkers from around the world to come to Canberra for several months and train together during the study.

The walkers were randomized to three-week training blocks under three different conditions: a traditional high-carbohydrate diet; a LCHF diet with 75 to 80 percent fat, 15 percent protein, and less than 50 grams a day of carbohydrate; and a “periodized” group that did some workouts with full carbohydrate stores, others while carb-depleted, and sometimes slept without refueling carbohydrate stores after an evening workout, a tactic recently shown to boost endurance performance. All the food was provided—and weighed to the ounce—by AIS staff, ensuring that the athletes followed their dietary plans exactly.

The results? Of the four athletes randomized to the first session of LCHF, Dunfee set his national record two weeks later, and South African walker Marc Mundell broke the African record in the same race. Still, Dunfee is hesitant to draw a direct link between the diet and his performance. After all, he was training hard with world-class peers. “It’s also clearly an individual thing,” he adds: a third member of the group felt terrible throughout the three-week period and dropped out of the 50-kilometer race. Dunfee also notes that his heart rate was higher and his times were slower during training, and that he switched back to carbs two weeks before the race. “In that time I was crushing my workouts,” he says. “I don’t know whether training on [the LFCH] diet was an additional stressor that made training seem like lower quality than it actually was, and I physiologically adjusted to the extra stress.”

The actual results won’t be tabulated until the runners have tried the different diets, and will be based on metabolic data and controlled 10-kilometre time trials. They’ll be available in time for Dunfee and his peers to decide which approach they want to use heading into this summer’s Olympics. Of course, they won’t settle the debate. Laursen, for example, believes it takes months, not weeks, to adapt to a high-fat diet and get over initial problems like the loss of high-intensity surging ability.

Whatever happens, we’ll soon know more about how the body responds to different diets than we do right now. “Nutrition is a cyclical science,” Burke says. “You’d be surprised at how many ‘new ideas’ are simply old ideas reimagined. So there is always the chance that it’s simply ‘hula hoop season’ again, and it will be a craze until it’s not. But there’s also a chance that new science will emerge.”

The brain’s tolerance for pain may be the deciding factor in how far we can push ourselves

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If you’ve ever experienced that sensation of powering up the last hill of a long run— when your legs feel like cement and your lungs are heaving, you’ve probably wondered how much your body can actually take. Could you dig deeper, even when your legs are telling you to stop?

Your own stopping point may have as much to do with your tolerance for suffering as physiological strength. We are accustomed to thinking that our limits are physical and that the way to get stronger is by pushing harder and going longer. But the brain’s tolerance for pain may play a significant role in how far one can push into that dark place.

Lex Mauger is a professor of exercise science at the University of Kent. He believes that pain tolerance may be the key to performance. “My latest research suggests that a participant’s tolerance of exercise-induced pain can be used to predict their endurance performance,” Mauger says.

But pain tolerance isn’t necessarily just something you’re born with. Mauger believes that, like aerobic capacity or lactate threshold, tolerance is malleable. “For training, I think feeling pain is part-and-parcel of this, and learning to tolerate pain in training means you will likely deal with it better when it counts during competition.” Mauger is even looking into whether additional performance gains can be made by adding additional levels of pain training, a sort of HIIT for suffering.

Exercise related discomfort is part of endurance sports. But it’s the management of that discomfort that separates individuals. A 2007 survey of Olympic cyclists, presented in the Journal of Sport Behavior, concluded that, “there is one element that all athletes who wish to excel must confront...exertion pain.” In the study, those surveyed didn’t speak of not suffering but rather of managing it, using mental strategies to cope with the suffering.

How? They talked themselves out of it.

To lessen the agony of exertion, the techniques the cyclists used included goal setting, imagery, and positive self-talk. Feeling prepared for a race or completion also seemed to minimize the feeling of pain.

While pain may not be a one-way ticket to athletic greatness, tolerance for physical discomfort may allow endurance athletes to fully tap their potential.

Everybody hurts, so increasing your threshold may not move you from back of the pack to podium – that may have to do more with training and genetics – but it might move you up a few places.

How Should Runners Fuel?

The somewhat simple answer to a popular question

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Should runners fuel according to distance or time? That simple question recently launched a lively debate on Reddit’s running thread. “I've seen here several times that you shouldn't need to fuel anything under a half marathon distance,” wicked_lion posted. But “wouldn't it matter more time vs distance?”

We posed the question to Matt Fitzgerald, author of The New Rules of Marathon and Half Marathon Nutrition. The short answer, he says, is you can run fuel-free without hurting performance for “somewhere around an hour, an hour 15.” Meanwhile, 10 miles is the shortest distance studied where carbs aid performance. So if you’re running more than around an hour or 10 miles—whichever comes first—you should plan to ingest carbs during your workout. (At 7:30 pace, you’ll run 10 miles in 1 hour 15 minutes.)

However, there has been some evidence that periodically rinsing your mouth with sports drink for five to 10 seconds can improve performance in exercise lasting 30 minutes to an hour. Researchers believe the solution may somehow trick the brain into believing it received the extra fuel, causing you to adjust your output accordingly. Researchers also saw similar performance benefits if athletes ingested the drink instead of swishing it, but noted that at high intensities, ingestion could cause GI issues that swishing shouldn’t.

As for how many carbs runners should get in if they’re going longer than an hour, “the magic number is 60 grams per hour,” Fitzgerald says, regardless of bodyweight or intensity in general. That’s about the max rate intestines can absorb glucose, although some studies have shown that the body can absorb even more carbs per hour when you add fructose and maltodextrin to the mix, whether those carbs are in liquid, gel, or low-fat, low-protein, low-fiber energy bar form.

But absorption is also dependent on how well you’ve trained your gut to handle carbs. If you really want to reap the performance benefits of carb ingestion on race day, “dedicate at least some time to training with a relatively high carbohydrate intake,” wrote renowned sports nutrition researcher Asker Jeukendrup in a 2014 summary of research conducted on carb intake during exercise. “Anecdotal evidence in athletes suggests that the gut is trainable and that individuals who regularly consume carbohydrate or have a high daily carbohydrate intake may also have an increased capacity to absorb it.”

At this point, however, it’s unclear exactly how much of a performance boost carb-trained athletes will actually get on race day. But Jeukendrup and his colleagues believe maximizing carb absorption is important enough that it will play a role in an athlete’s ability to break the two-hour marathon barrier.

If you’re not gunning for a PR, don’t fret too much about nailing that 60 grams per hour mark. “Your fueling doesn’t have to be perfect,” Fitzgerald says. “You just want to basically do the right things.” If you are going for glory, carb intake comes down to what you can tolerate over the distance you’re running.

“When I was at my best, I ran the half marathon a little under an hour 15 minutes,” Fitzgerald says. “I went back and forth saying, ‘Am I’m gaining more than I’m losing by not taking in carbs,’ and I finally settled on not needing them. You have to experiment.”

A new trend of group treadmill training is being modeled after the success of other machine-based cardio classes

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The instructor’s voice boomed through the speakers, telling us to “keep moving,” as the pounding bass of hip hop music vibrated against the exposed brick walls. Everyone around me dripped with sweat while their legs churned. It felt just like a cycling studio—except without the bikes.

Instead, I was on a treadmill, keeping a 6:45-mile pace at a 6-percent incline, about half-way through a 45-minute “endurance” class at MyStryde, a newly opened running studio in Boston. Yes, I said running studio. MyStryde is part of a new trend of group treadmill training that’s being modeled after the success of other machine-based cardio classes.

Wearing a headset with a microphone, my instructor Katie told the group to imagine we were running up a hill, almost to the crest. “C’mon Stryders (what they call anyone who attends a MyStryde class), move your bodies! Let’s go!”

She was peppy and upbeat, and at that very moment, I hated her. Yet there’s no doubt that I was pushing myself harder than if I were working out by myself on a treadmill.

MyStryde is the creation of 28-year-old Rebecca Skudder, a former collegiate runner who got tired of her desk job in downtown Boston and began planning several years ago to start a treadmill gym. It opened in January on the site of a former clothing boutique in the city’s North End. It’s the first of its kind in Boston—and one of the few anywhere in the country.

Her intent was to “create a spin environment, a motivating environment” for runners, she says.

The concept of a modern running studio first started in 2014 in New York City, when Mile High Run Club opened its doors on East 4th Street in Manhattan, offering classes on its 36 treadmills. It now gets 1,700 customers per week, says founder Debora Warner, nearly 90 percent of them repeat visitors.

“I’ve been surprised to see how much enthusiasm there is not only for the classes but also our brand. I see runners all over town wearing our t-shirts,” Warner says.

Some traditional-style gyms have also picked up on the group treadmill concept. High-end chain Equinox, for instance, offers classes at some of its clubs across the country, as does Barry’s Bootcamp, and FitMix in Los Angeles.

During the class I attended at MyStryde, which was on a Thursday night and cost $15, only three of the studio’s 12 treadmills were empty. To my right was a woman training for the Boston marathon, moving at a quick pace. I was curious to see exactly how fast she was running—but the atmosphere is intentionally kept non-competitive, and workout stats aren’t shared.

“A big part of this place is to make sure everyone feels comfortable,” Skudder explains. She adds that she wants runners to see the studio’s classes as an alternative to a typical road workout, in any season.

“We’re just trying to spread the love of running. The feeling you get here is a little bit different than on the road. You’ve got the music, you’ve got the instructor,” she says.

Virtual Runner is just one of an ever-growing list of apps aimed at improving indoor workouts through a virtual experience

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Last August, more than two dozen runners competed in the famed Falmouth Road Race in Massachusetts without ever setting foot near the start or finish line. They ran it remotely, on treadmills scattered in gyms and homes across the country, through a virtual running app that let them see a high-definition, pre-filmed video of the course as they progressed.

It was the first virtual race of its kind ever run. More importantly, it proved what much of humanity once thought was impossible: that modern technology can actually make treadmill workouts bearable.

The app the racers used is called Virtual Runner, produced by the Massachusetts-based company Outside Interactive (no relation to this publication). It offers a selection of more than 10 different running routes, including a four-mile historic run among the Washington, DC monuments, the route of the Mount Desert Island Half-Marathon in Maine, and of course, Falmouth.

Virtual Runner won’t make you feel the wind blowing in your face but, “it makes you feel like you’re making progress on a treadmill. And that makes the time go by quicker,” says Outside Interactive CEO Gary McNamee.

Virtual Runner is just one of an ever-growing list of apps aimed at improving indoor workouts through a virtual experience. Another, called Treadmill Trails, takes runners and walkers on a 30-minute workout down famous footpaths in Central Park, Big Sur, and Yosemite, and on the Appalachian Trail.

The app RunSocial, which uses the slogan, “How to beat the boredom,” lets you virtually run one of its 15 high-definition filmed courses three different treadmill-bound ways: alone, in a real-time public event with people all over the world, or in a private one organized with friends. Each runner is represented by an avatar on the screen and, like a video game, you can pass them or get passed, depending on your speed. RunSocial recently announced that runners will soon be able to use the app to compete remotely in April’s London Marathon—just as British astronaut Tim Peake did from the International Space Station last year.

Another popular, fairly new app is BitGym which works with just about any cardio machine, including ellipticals, exercise bikes, and treadmills. It offers more than 100 courses, from rugged mountain trails in Northern Italy to the streets of Chicago. BitGym tracks your progress by capturing your movements through your mobile device’s camera, and synchs your pace to the speed of the video. By contrast, Virtual Runner and RunSocial need a separate footpad or pedometer for automatic speed control.

BitGym, which got its initial funding on Kickstarter, is aimed mostly at “people who work out in their homes who know how painful it can be do to on a machine, and are looking for anything that will make it better,” says Alex Gourley, one of the app’s creators. About a third of its tours include recorded video and audio of cardio coaches, who are supposed to motivate you throughout the workout.

McNamee says he’s working on possible partnerships between Virtual Runner and 20 different road races over the next couple of years for virtual entries, like at Falmouth.

“It’s a great way for races to show off and preview their event. For Falmouth, we’re basically giving them a seven-mile commercial.”

It can also mean potentially unlimited revenues for bigger, more famous races, as thousands of people participate around the world from their treadmills, real-time. “How about a million people walking, running, or crawling the Boston Marathon in 10 years?” McNamee asks.

Is Iron the Answer to Training at Altitude?

Why Aussie athletes often turn to supplements when living high

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Athletes live and sometimes train at high altitude for one main reason: it stimulates erythropoiesis, or the production of red blood cells and hemoglobin, the protein inside red blood cells that carries oxygen around the body. That extra hemoglobin should bring more oxygen to muscles, which should lead to improved muscle function and endurance when an athlete competes at a lower altitude soon after leaving the mountains.

The problem is, individual athletes respond differently to altitude. Even after the generally recommended four weeks of living between about 5,200 to 9,800 feet, some athletes won’t show much increase in hemoglobin. That’s why researchers have begun experimenting with iron supplementation.

“Iron is needed by the body to make haemoglobin,” wrote Dr. Laura Lewis, a researcher at the Australian Institute of Sport, in an email to Outside. “Without iron, the body will not be able to make more [haemoglobin] so adaptation will be compromised.”

Iron deficient athletes could certainly benefit from iron supplementation, Lewis wrote, but so might athletes with normal iron stores. “Iron supplementation can help facilitate adaptation. You won’t get a faster response, but you increase your chances of getting a positive response rather than none at all.”

Athletes at Australia’s Institute of Sport are currently advised to get a blood test and iron screen about a month before going to altitude, explains Lewis. A sports doc reviews the results and decides if they should supplement or not. If an athlete’s low, they usually start supplementing two weeks before going to altitude; if they’re normal, they’ll start at altitude.

“Our typical supplementation strategy is an oral supplement taken with Vitamin C to help absorption,” Lewis wrote. In a study she co-authored that was published last August in the open-access scientific journal PLoS One, athletes who supplemented with 210 milligrams of iron daily during two to four weeks at altitude increased their haemoglobin mass significantly more than those who supplemented with 105 milligrams or none at all.

“I would advise all athletes who are going to be spending longer than one week at altitude to consider iron supplementation,” Lewis wrote. But only after an iron screening and consult with a sports doctor. The worst thing an athlete could do is start loading up on excess iron. “More is not better,” she wrote, “as new data suggests that not only are high oral does not well tolerated, but they can also impair future absorption.” Too much iron in the body can also lead to a host of health problems, including osteoporosis and metabolic syndrome.

“Iron can be an important component for a successful altitude experience but is not a magic bullet,” Lewis wrote. You’ve got to “get all the basic ingredients right.” Like getting there sans injury, and relatively fresh. “Eat well and train appropriately up there and respect the altitude—it’s a training stimulus in itself (even at rest) so don’t feel like you have to do more.”

It turns out there's an entire field of science dedicated to studying how and why boobs move

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All breasts, great and small, are comprised of subcutaneous fat tissue, mammary glands, and nothing else. They are bound to the torso by what are known as Cooper’s ligaments. These ligaments have no stabilizing function, they merely connect the breast tissue to the collar bone and muscles of the upper chest. This means that any and all natural support for breasts comes from your skin. And it turns out there is an entire field of science dedicated to studying how and why boobs move and how this movement affects performance. It’s called breast biomechanics, or as I prefer, the science of the jiggle.

The University of Portsmouth’s (UP) Department of Sport and Exercise Science is the leading breast biomechanics research group in the country. Dr Joanna Scurr and her team (which includes several men), use state of the art motion imaging and user surveys to study everything from types of breast movement to the effect of perceived breast pain on performance and sports participation. Here are some of their findings:

Breasts Move a Lot

Their 2014 study titled “Multiplanar breast kinematics during different exercise modalities” found that most breast motion either occurs in the vertical direction or the mediolateral (side to side) direction. Jumping activities tend to cause more vertical motion, while activities involving agility tend to generate more mediolateral motion. “Sixteen 32D participants had markers attached to their right nipple and torso. Relative multiplanar breast displacement was calculated during bare-breasted treadmill running (10 kph), maximum countermovement jumping and an agility t-test.”

Painful Movement Turns Many Away from Exercise

A study published in January of this year found that while sports bras do control breast displacement caused by exercise, perception of the fit and comfort of the bras were better indicators of reduction of breast pain than the measured volume of discomfort. Their most recent study, which was published in February, looks at the impact of breast pain on sports participation. It found that about half of the school-age girls surveyed might be avoiding sport because of “embarrassment or pain caused by their breasts.” A subset of the group works to develop breast health curriculum aimed at getting girls and women in better fitting sports bras, thus increasing sports participation.

Sports Bras Help, But They Could Be Better

Most importantly, the UP research has identified that the type of bra worn, and its fit, can change the way you run. There has yet to be a study looking at impact of breast movement on fatigue over a long effort (say, a marathon) or a study looking at non-running based sports. But, the Portsmouth group has several research projects they are seeking commercial partners on, meaning a better bra could be headed your way soon.

The Science Behind Falling Out of Shape

Or why you should never, ever stop training

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When you’re in peak physical condition, you feel like a superhero—like you could go forever, outpace a cheetah, or lift a VW Bug. But your superpowers are ephemeral; the second you stop training, they start to fade. We asked sports physiologist Iñigo Mujika to give us a quick rundown of what’s behind the glory and the fall. The takeaway: you should never, ever stop training for more than two weeks if you can help it. Here’s why.

When you start working out, wonderful things begin to happen. Take strength, for instance. In just a few sessions, you’ll get stronger—but not because your muscles are any bigger yet. “The initial gains take place because of neuromuscular adaptations,” Mujika says. In short, your brain gets better at communicating with your muscles, learning to use them more efficiently. It’ll also start to recruit more of them, so power ultimately increases, too.

Just over a week of endurance training—often described as at least 30 minutes per day, five days a week of upping your heart rate to at least 60 percent of its max— increases your plasma and blood volume. That’s part of the reason why, a few weeks into a training program, your heart rate won’t spike like it did when you first started running, or whatever your sport may be. And you’ll get better at dissipating heat through sweat.

Keep up your training, and you'll gain muscle mass and strength. You’ll also fine-tune your cardiovascular system; after six months of endurance training, it’s possible to increase blood volume by as much as 27 percent.

All of those adaptations lead to peak performance. But the catch: there’s no peak preserving pill, and all of those benefits quickly erode when you stop moving. “When you stop training, almost immediately—we think three days—you lose plasma volume and blood volume in general,” Mujika says. “Your heart rate for a given intensity increases.”

After about 10 days to two weeks, your VO2 max, or the max amount of oxygen you can take in during exercise, will start to drop at a steady rate of about 0.5 percent a day. Two weeks off, and your brain’s ability to recruit muscle will drop, by about one to five percent. That’s not much. But it can cut power in sports that require fine-tuned movements for optimal performance, like swimming.

After three to four weeks off, your muscles will start to atrophy. Your body will increase its reliance on carbs rather than fat for fuel while simultaneously upping its capacity to store fat. In other words, your ability to burn fat slacks off at the same time it becomes easier to get fat.

That’s how metabolic syndrome gets started, Mujika says. Physical inactivity leads to becoming overweight, then insulin resistant, then diabetic. “The symptoms experienced by athletes when they stop training are the same,” Mujika says, “but on a very small scale.”

That doesn’t mean you can’t ever take a break. Breaks are necessary to avoid overtraining and burnout. Mujika tells his athletes, including three-time Olympic triathlete Ainhoa Murúa, to take two weeks completely off from training at the end of their seasons, then spend two weeks doing physical activity that’s not sport specific. For Murúa, that might be hiking, SUP, surfing, playing tennis—anything but swimming, biking, and running. “After two weeks of that we start training into more sport-specific exercise,” Mujika says.

Expect it to take twice as long to get back into shape as the time you’ve spent being inactive, Mujika says. With a few exceptions: “heat training can accelerate plasma volume expansion,” he says. And if you’re starting from scratch, you might have an advantage over people who are. “There are some indications there’s some kind of muscle memory,” Mujika says. Just like people who’ve already ridden a bike will pick it up faster than those who haven’t, it’s possible “the more trained you’ve been before, the quicker you get back into form in terms of muscular strength and power.”

How Much Protein Do You Really Need?

More is not always better

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Americans are obsessed with protein. Protein powders make up 70 percent of the country’s $6.7 billion sports nutrition market, according to market research firm Euromonitor International, and the high-protein diet has officially become the nation’s favorite. But while athletes need more protein than the general population, experts say, there is a point of diminishing returns.

“Athletes are better off consuming 1.6 grams of protein per kilogram of bodyweight per day [over the government’s recommendation of 0.8 grams],” says Stuart Phillips, director of McMaster University’s Centre for Nutrition, Exercise, and Health Research in Ontario, Canada. For a 150-pound athlete, 1.6 grams per kilo works out to about 109 grams of protein daily, or 2.5 chicken breasts. “That’s not to say you can’t consume more,” Phillips says, counter to theories that eating too much protein can cause kidney failure or bone loss. “But after about 1.8 grams per kilogram per day, the benefits start to level off.”

Those benefits include muscle maintenance and repair, as well as support of the health of ligaments, tendons, and bones—parts that are primarily made of a protein called collagen that can also break down during exercise.

“Think of your muscles like a brick wall; you put new bricks in to keep it fresh and pull bricks out at the same time,” Phillips says. The bricks are amino acids, the compounds your body breaks food protein into. Phillips says two proteins found in milk make the best new bricks: whey, “a rapidly digested protein that turns on the rebuild phase” and casein, a more slowly digested protein.

Recent studies have found that consuming protein during exercise doesn’t have much effect on performance or recovery, though Phillips points out it may be beneficial during ultra-endurance events like Ironman or an ultramarathon.

Protein eaten before a workout can kill hunger and may help attenuate muscle breakdown, but research on pre-exercise protein benefits is far from conclusive. After exercise, however, “your muscles are like sponges. They’re ready to soak up nutrition and they’re ready to rebuild,” Phillips says, though researchers are still debating if there’s an optimal time post-workout to fuel up.

The kicker: Power athletes like weight lifters don’t need more protein than any other athlete. “If you get 1.6 to 1.8 grams per kilo per day, it doesn’t matter if you’re lifting six days a week or two, or if you’re running two or six or seven,” Phillips says. After that amount, the benefits don’t increase.